Thanks for that Jim,
Well we plan on using some on site "Shot Gun" coax (about 8 gauge diam)
as the ladder line conductors with a 6 inch spacing. Which on a test
length gave us around the 450 ohm impedance we require.
I dont know the diameter of that WD1a wire but suspect it is quite small
which would make home made 450 ohm line spacing very small indeed.
Your method of supporting using the wood clamps sounds a good idea as we
were concerned about the plastic clamps breaking due to flexing and UV
deterioration.
If our conductors fail through the flexing then we may bite the bullet
and buy some Aluminium wire as Rik N6RK uses.
All useful info though and thanks again Jim.
73
On 06-Jan-18 20:38, Jim Garland wrote:
Vic, I've had nothing but bad luck in trying to support long horizontal lengths of ladder
line. In my case, I have two 720 ft bidirectional beverages, which I initially made of
heavy duty commercial ladder line. I supported the line with wood 4"x4" posts,
spaced sixty feet apart, using the little plastic ladder line clamps, sold in the US by
DX Engineering.
After only a month or so, the plastic clamps broke apart because of the
repetitive flexing of the ladder line in breezes. I replaced the clamps with
wood clamps, screwed into the top of the posts. These survived with no problem,
but the ladder didn't. After six months or so, I started having breaks in the
line from the flexing, and after spending two years repeatedly repairing the
line, I gave up and threw away all 1500 feet of the stuff.
Finally, I settled on WD1a military surplus field telephone wire, available
from many sources for about $50 USD in half mile lengths. I use two parallel
lengths of the wire, threaded through twin ceramic insulators screwed into each
4x4 wood support (available from a farm supply store), with a pulley at the far
end to equalize tension in the two lengths. In three years, it has worked
perfectly, with no problems at all.
I'm not disparaging ladder line (or the plastic clamps) at all. The commercial
stuff just isn't designed for long horizontal lengths.
73,
Jim W8ZR
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Vic
Sent: Saturday, January 06, 2018 01:17 PM
To: topband@contesting.com
Subject: Topband: Supporting Ladder line
Has anyone idea's of how to support a long (750 ft) length of home made
450 ohm ladder line ?
Is it possible to use it supported from posts in a vertical orientation or will
that introduce
imbalance.
I would prefer not to have it supported horizontally due to added cross arms
being
required.
Have scoured internet sources but their appears little information available on
the subject.
I plan to feed a Marconi Tee Vertical (Hairpin Matching) with 9:1 transformers
at each end
of the ladder line enabling use of 50 ohm coax at each end for convenience.
73
Vic
G4BYG (G6M)
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|